Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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Page 1 of 4

1. For obtaining high COP, the pressure range of compressor should be

Any value

Low

Optimum

High

2. In a lithium bromide absorption refrigeration system

Lithium bromide is used as a refrigerant and water as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

None of these

Water is used as a refrigerant and lithium bromide as an absorbent

3. The value of C.O.P in vapour compression cycle is usually

Any one of the above

Equal to unity

Always more than unity

Always less than unity

4. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant pressure

Involves no change in volume

Takes place at constant temperature

Takes place at constant entropy

5. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Carbon dioxide

Brine

Freon

Ammonia

6. Which of the following is not a desirable property of a refrigerant?

Low boiling point

Good electrical conductor

High risibility with oil

Large latent heat

7. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Dew point temperature

Relative humidity

Dry bulb temperature

8. The freezing point of sulphur dioxide is

-75.2°C

-56.6°C

-77.7°C

-135.8°C

9. Freon group of refrigerants are

Inflammable

Non-inflammable and toxic

Nontoxic and non-inflammable

Toxic

10. A bootstrap air cooling system has

One heat exchanger

Three heat exchangers

Four heat exchangers

Two heat exchangers

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11. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Equally

Less

12. The domestic refrigerator uses following type of compressor

Axial

Piston type reciprocating

Miniature sealed unit

Centrifugal

13. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

2.33

3.33

4.33

1.33

14. Critical temperature is the temperature above which

A gas will never liquefy

Water will evaporate

Water will never evaporate

A gas will immediately liquefy

15. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

2.15

5.12

16. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₂/ (T₂ - T₁)

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

17. The operating pressure for refrigerating units using R-12 as a refrigerant is

30 bar

15 bar

8 bar

2 bar

18. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Super-cooling

None of these

Normal cooling

Sub-cooling or under-cooling

19. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.6

0.376

0.67

0.4

20. The boiling point of ammonia is

-77.7°C

-10.5°C

-30°C

-33.3°C

Page 3 of 4

21. In a refrigeration system, the expansion device is connected between the

Compressor and condenser

Condenser and receiver

Evaporator and compressor

Receiver and evaporator

22. Rating of a domestic refrigerator is of the order of

5 tons

40 tons

0.1 ton

10 tons

23. A thermostatic expansion valve in a refrigeration system

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

None of the above

24. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Superheated vapour

Wet vapour

Saturated liquid

25. The minimum temperature to which water can be cooled in a cooling tower is

Dew point temperature of air

Ambient air temperature

Wet bulb temperature of air

Dry bulb temperature of air

26. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 1

1: 9

9: 1

1: 3

27. Highest temperature encountered in refrigeration cycle should be

Much below critical temperature

At critical Temperature

Above critical temperature

Near critical temperature of refrigerant

28. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(B) Heat stored in the human body

(D) Difference of (A) and (B)

29. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

30. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Zero

Negative

Positive

None of these

Page 4 of 4

31. The vapour compression refrigerator employs the following cycle

Rankine

Carnot

Reversed Rankine

Reversed Carnot

32. The capillary tube, as an expansion device, is used in

Water coolers

Domestic refrigerators

All of these

Room air conditioners

33. The bank of tubes at the back of domestic refrigerator is

Capillary tubes

Evaporator tubes

Refrigerant cooling tubes

Condenser tubes

34. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect liquid refrigerant and prevent it from going to compressor

Detect liquid in vapour

Superheat the vapour

Collect vapours

35. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

36. Cooling water is required for following equipment in ammonia absorption plant

Condenser, absorber and separator (rectifier)

Condenser

Evaporator

Absorber

37. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(D) Both (A) and (B)

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

38. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

Less

More for small capacity and less for high capacity

39. Most thermostatic expansion valves are set for a superheat of

10°C

15°C

20°C

5°C

40. Which of the following cycles uses air as the refrigerant?

Stirling

Bell Coleman

Ericson

Carnot

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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